Hydraulic speed control apparatus for regulating the fuel supply for combustion engines



Aug. 12, 1952 A. ROOD ET AL ONT 2,606,419 HYDRAULIC SPEED c Rol. APPARATUS FOR REGULATING THE FUEL SUPPLY FOR COMBUSTION ENGINES 2 SHEETS-SHEET l Filed Feb. 8. 1947 A. A. ROOD ET AL ONT Aug. 12, 1952 2,606,419 HYDRAULIC SPEED C ROL APPARATUS RoR REGULATING THE FUEL SUPPLY PoR coMBUsTIoN ENGINES 2 SHEETS-SHEET 2 Filed Feb. 8. 1947 RWE,

Patented Aug. 12, 1952 HYDRAULIC SPEED CONTROL PPARATUS FOR rRIE GULATIN G THE FUELl SUPPLY FOR COMBUSTI'ON' ENGINES .Alvin A. Rood,V Cleveland,

Euclid, Ohio, assignors and :John F. Campbell,- to The -Weatherhead- Company, Cleveland,v Ohio, a corporation. of

Ohio

Application Februaryf 8, 1947',v Serial No. 727,366

11 Claims.

This .iinventionzrelates to ltheacontrol of .internal combustion .engines .such as thatora. turbo jet.v

engine yusedin aircraft. More aparticularly, this invention .relates to novel uidfactuated means for controlling fuel supply and other conditions of the engine.

It is` an object .of this'- inventionto provide means to remotely control atzthrottlezfinl the .engine fuel supplywhich operates in conjunctionwitha valve rsystem that maintains ia constant; pressure ldrop acrossthe throttle thereby: permitting uniformity of action of the z remote .control .meansindependent of resistance of. fuel .flow into .the. engine.

Another object'`4 residesf in preventing the i `remotely controlled throttle from'. moving f to vcut oli' the fuel supplyentirelyandtinwthe provision of manuallyl controlled meanswhichoperate. to cut off fthe fuel supply -if the operator 'so desires.

Anotherf'object is thezprovisionl of means to perm-it manual selection Aof .engine speed fand means to' automatically maintain engine speed-atlthe selected value.

A `further vobject of f one embodiment of our vinvention is' t0 make a` remotel control l.of .the throttle-sensi-tive'to small persisting speedvariations,-'the control beingrrelatively insensitive vto very I small oscillatory speed variations.

A further object of one embodiment of ourl invention lies in thef-protectionof the'engineffrom too rapid Yaccelerationand excessive combustion chamber temperatures. We 'accomplish this object vbyv providing :means inthe controlsystem which vslow down the acceleration of the engine relative to the deceleration.

A furthei'object of another embodiment of our invention lies in the' Vprovision V-of 'a -pressu're controlled governing switch @and remote control means to position said switch' inforder' to energize an electric circuit that may control propeller pitch governing motor or any othern controlling device.I

Thesaand' oth'erobjects willloeapparentas the following detailed description ofi our invention proceeds.

In the drawings:

Fig. ris-"aschematic view' of oneembodiment showing the iiuid fand hydraulic circuits; and

Fig. 2 is a'schematicl drawing of a second'modication of ourinvention.

In 4the Amodification shown inFig; 1, there isfa hydraulic circuiti-.Which -controls the throttle. in such ya manner ras.'A to. .maintain ther speed of*` the turbine constant .representing a. given setting of thev manually'.` controlled.l condition'.I lever; The

speed itself is selected-by thecondition lever-in` accordance'withthework to be done andthe actual speed .attained .by the `:engine `:sensed .fby a. variable vpressure Apump Idriven 4by the; engine,

which pump is'part of-ahydraillicy control Inecha-y nismn that .automatically-y adjustsI .fuel flow until. theselectedspeed'is attained.

The constant speed.hydraulic...circuiti which controls. the. `fuel W :operatesy in' .conjunction withan `electric s. circuit which'zcontrols the load` irr aA novel :manner so: thatthe :temperature irr'thev combustion chamber `of the `engine :is:rrriaintainedv ata preselected'value; The details-ici .the elec.- tric circuits :which maya be-'5. employedztoiaccome plishV .this 1 are fully. described: thencoependng.

application 1 of` -A...R.food; Sen No;V 711,961; led.

Nov..23, .1946; Basically,` this.iis;accomp1ished-Lbyj measuring -f the.. temperature the. combustion. chamber; correctingit forr'heat transferV lag; .comparing the :corrected temperature with"v :the selected temperature,` causing. any` .'diiierenceA thereinv tto: increase :or: decrease pitch. of the Ipropeller thereby increasing or 'decreasingztheiloatt proportionately; For example, if the1actua1ntemperature is higher than the selected temperature' thenovel. arrangement.. described the.: aforesaid.` l co pending application will` automatically decrease the pitch'- of theA propeller 1 thereb'yfdehcreasing the: load on the "turbine `tanda'cause the: temperature.` in thencombustionzchamberftodrop This f arrangement r particularly reflective.'v be-` cause it Lisrinr'combination .with .theconstant speed fuel supply circuit.' .This 'combinationzmakes it possible to' automatically 'compensate .fori diieriences in engine-operating conditions due-tovariations-.Lin altitude and :alsoivariationsLofzlfuel :ref quirementsrdue toichangeszin engine eciencyrat variousispeeds.

The @circuitsfwhichzcontrol i the :fuel :can ;beffdi'' vided .intotthreeff major-divisions; .rst; Vtheouel circuit 1 itself;i second; the :hydraulic :control :or servo'icircuit; andthirdgthe sealedt-.throttle:actu1-1V ating circuit; Although We ,haveillustrated lidia#-V grammatically.A one typefof engin-ewhich `mayfbel employed; .it will .befunderstood' that .wee have merely `done :this to illustrate: an .application ;o:fv our. invention, andV although the. jet' or :turbine engine presents', certain .special .problems.-twhch:` are.,solvedrby oursapparatus; .wefdo.:net ilimitzoun.` selvesv to. .utilization .of f: ourxnovel control means` with -anyrone `engi'ne..design unless Lsaidzdesign claimed. The :engines may lhavefa `gas turbine LI which -is driven by burning-Lof. fuelumixedmvithiaiii i111 theycombuston chamber; One-or more'fair: compressorxstages 2: :may .fbleidriven by the turbine shaft 3 to supply the necessary air. The turbine shaft usually drives a gear reduction unit 4 which turns the propeller 5. We contemplate the use of a variable pitch propeller, one form of which may have an electric motor to change propeller pitch indicated generally at E.

The main fuel supply line ID connects to the fuel pump which may be a positive displacement pump and which supplies fuel under. pressure to line II. The throttle is automatically positioned as will be described presently and acts to determine the amount of fuel which flows into line I2 and hence into the combustion chamber at I3. A cut-off valve, spring urged to a closed position, is normally held open by the fuel pressure but if that pressure drops below a predetermined value, the cut-off valve will close and prevent fuel from entering the combustion chamber at low pressures. In order to make the amount of fuel which flows into the combustion chamber a direct function of throttle position independent of fuel pump pressure and of the orifice resistance in the chamber, it is desirable to have a constant pressure drop occur across the throttle. In order to accomplish this a constant pressure difference by-pass valve and a pressure difference control pilot are provided. The pressure difference valve fits in a cylinder one end of which connects by line IIa to the throttle inlet line II. The valve close oi passageway I8 so that passageway chamber I6 behind the valve to gradually build up and almost equal that in line IIa. Spring I1 urges the constant pressure difference valve to the right to close a by-pass line Ina by-passing uid from line Il to supply line IB, so that the higher the pump pressure the greater the bypass. A line I2a leads from the throttle outlet I2 and fuel in this line is at the pressure necessary to force fuel through the nozzle in the engine. Pressure in line I2a urges the pressure difference control pilot to the right in the drawing so that it tends to close off the passageway I8 and hence tends to seal off the left end of the constant pressure difference by-pass valve, urging the by-pass valve to the left.

Assume that for some reason or other pressure of the fuel entering the combustion chamber through passageway I2 does not change but that fuel pressure in passageway II from the pump increases. The increase in pressure in line II will cause the constant pressure difference valve to move to the left which will tend to by-pass high-pressure fuel by means of line IIa into the 10W pressure line Illa, thus reducing pressure in line II. The valves are designed so that this action continues until the pressure dierence across the throttle, that is between lines I I and I2, is at the predetermined value. Assume now that the pressure in line II from the fuel pump remains constant but that pressure in line I2 leading from the throttle to the combustion chamber increases, dueto a restriction in the nozzle, for example. It will be noted that a certain amount of fluid from line Ila always tends to pass through orifice I5 in the pressure difference valve and pressure within the chamber I6 and behind the valve tends to equal the pressure in the high-pressure fuel line I I. Under normal operating conditions the pressure difference pilot does not completely close off passageway I8 so that passageway I8 can communicate with a line Illb connected to the low-pressure side of the fuel pump. However, due to the throttling action at the pressure difference pilot there will be a pressure built up behind the pressure difference valve which pressure will augment the force of spring I'I tending to move that valve to the right and tending to shut oi the by-pass between chamber Ila and low-pressure line Ia. Now, if the pressure increases in line I2 it is necessary to increase the pressure in line Il an equal amount to maintain a constant pressure drop across the throttle. This is accomplished as the pressure difference pilot moves to the right under the increased pressure in line I2a, tending to restrict the exhaust from chamber I8 into the low pressure line Ib and causing more pressure to build up behind the constant pressure difference valve. That valve now moves to the right and decreases the by-pass from line IIa into the low pressure line Illa. The valves are arranged so that this action continues until pressure from the fuel pump in line Il increases by the same amount that the pressure in the nozzle line I2 was increased. Thus, it can be seen that the constant pressure difference valve will maintain a constant pressure drop across the throttle regardless of whether there is a pressure change in the fuel pump line II or in the delivery line I2 to the engine,

or in both lines.

Having completed the description of the fuel feed circuit, the hydraulic control pressure circuit and its actuation of the sealed throttle actuating circuit will be described. In the modification shown in Fig. 1, a sump tank which attains a supply of oil or other fluid for actuating the control circuit is illustrated schematically in the drawing. A pair of pumps which may be driven by the engine, one being arranged to deliver constant `pressure and the other being arranged to develop a pressure which is proportional to engine speed are provided. The constant pressure pump discharges into the line 20 and forces fluid through the orice I5, pressure regulation being afforded by the regulating relief valve R which by-passes line 2I to exhaust line 22. The constant pressure fluid is conducted by means of line 23 to one side of a governor circuit selector shuttle valve. The variable pressure pump discharges in the line 24 at a pressure which is proportional to engine speed squared. A variable circuit relief valve V may be provided to limit the pressure in line 2li. The flow of fluid in the variable pressure lines 24 and 24a is by-passed partially by a proled portion 25 of a selector valve into an exhaust line 22a. The selector valve may be manually positioned in any convenient means to regulate the pressure of by-pass and, as will be explained presently, position of the selector valve eventually determines the speed of the turbine. The selector valve may be positioned by a condition lever, the position of which may be calibrated in terms of the condition under which the pilot wishes the plane to operate as indicated on the drawings.

One side of the governor selector shuttle valve is acted upon by constant pressure in line 23 and the variable pressure in line 24a acts on the other side. Under equilibrium conditions engine speed seeks a value such that pressure in the variable line 21m equals that in constant pressure line 23 for all selector valve positions. The constant pressure fluid enters passageway 26 and may be bled into either of lines 30 or 3| which form control lines for the sealed throttle actuating circuit. The sliding sealing piston 33 transmits changes in pressure in line 30 into a sealed chamber 35 which, in turn, transmits the change in pressure to chamber 36 on one side of a piston 31 which forms an acceleration-deceleration control unit.

is slidable to a limited extent and is urged to the left-by iluid pressure in chamber 36 and to the right 4by iiuid pressure in chamber 38 and also by springpressure of spring 39. This piston is provided with a fine spiral groove which permits a metered amount of oil flow through the piston. For example, if line 30 is opened to a source of iluid under pressure, sealing piston 33 moves left,

ametered lquantity of oil flows into chamber V4U.

and exertsa force against the sealed enddl of the proledthrottle. Conversely, if line 3l is opened to a `sourceof fluid under pressure the other end 42- of the throttle is acted upon by pressure in chamber 32. The position of the throttle is 'determined by the ow of iiuid in lines 30 and 3| which, in turn, depends on the position .of the governor-selector shuttle.

The acceleration and deceleration piston 31 modifies the eie'ct somewhat in -thefollowing manner. Assume thatequilibrium exists in that engine speed equals selected speed, whereupon the manual condition ylever is set for less speed. The by-p-ass effect of profile 25 of the selector valve'is then reduced so that pressure in line 24a increases andinitially exceeds that in the normally-constant pressure line 23. With this increase of pressure in line 24a, the'shuttle valve is moved up and bore 26 in theshuttle valve connects constant .pressure line 23 to line 3B, and line 3l is connected to exhaust by line 22h. Fluid tends to ilowv into line 30 and pressure builds up to the `right ofthe sealing piston 33. Thisincreases the pressure in chamber 35 and hencerin chamber 36 and tends to force fluid through the spiral groove in the piston 31. Furthermore, pressure against the end of piston 31 vin chamber 36-moves the piston to the left. Motionl ofthe piston to the left decreases the length of the restriction caused bythe spiral groove, the purpose of this action being to make deceleration somewhat more rapid than acceleration, in order to prevent excessive build up of heat `in the combustion chamber. The uid that ilows through the spiral groove added lto the fluid flow caused icy-motion ofthe piston -31 `to the left createsadditional pressure in chamber 40 which acts against the face 4l of the throttle causing itto move to the right. Whenthis occurs the profiled portion 43 of the throttle restricts the flow Yof fluid into-the line l2 and hence into the combustion chamberV at I3. Simultaneously, fluid is displaced-from chamberf32-into the'exhaustso there is no hydraulic block on` rthe throttle. As soon-'asengine speeddrops to the selected speed, pressure inline 24a drops to equal that in line 23. The shuttle valve vmay still be displaced from neutral'but this merely means that the throttle oversh'oots to return the shuttle valve; Thus the throttle hunts somewhat `until theselector valve centers whereupon there is no further motion of the throttle.

Once the selector valve is positioned to vselect a certain speed the'action ofthe variable pressure pump'against the governor'selector shuttle will continuously adjust the throttle to maintain the speed at the selected value.

The governor selector shuttle arrangement herein described makes available the Afull pressure in the constantpressure system for actuation of-the throttle which provides a verysensitive control. No matter how small the variation ink actualengine speed from selectedspeed may be, if that variation-exists Vover-any appreciable period,` of time the selector shuttle will 'move fto connect one of the throttle. control lines to full constantline pressure. This givesV a positive andv certain correction of very small speed variations, even though there might be some tendency for thevalves to stick or even though the system might tend to be somewhat sluggish in operation. The advantages of this arrangement can be readily understood if Vit iscompared with one wherein `the pressure variations in the variable pressure' line due to speed changes operate the` throttleY directly. If .thiswerethe case a slight variation in speed and its attendant slight variationin pressure in the variable pressure line might not be enough to break loose the throttle and move it. In our system we need only move ,a pilot valve which maybe relatively light .and free of movement, to apply'full constant line pressure to actuate theV throttle. Also, We can makethe landson ourpilot valve or selector shuttle valve slightly wider'thantheV ports which they close so that slight oscillatory variations in speed. will not be transmitted to the throttle and cause, undue hunting. However, if the slight variation in speed persists for any appreciable period of time, the shuttle valve will drift over lin the proper direction to correct .that variation.

Ifla. speed increase .is desired the selector valve is positioned to by-passlmore uid and'decrease the pressure in line 24a so that the shuttle vvalve is moved down. In .this case uid flows into line 3| and chamber 32 whereupon it acts upon the face 42- of the throttle to move the throttle to the left. This4 gives an increased fuel flow throughline l2 and more fuel reaches .the combustion chamber. It will also be noted that acceleration cannotbe .effected as quickly as deceleration because'when the throttle is moved to vtheleft vit forces fluid from chamber vlll against the left end of the piston 3l. This causes the piston to .move toA the .right and imposes the full length of the spiral groove in the pathl of huid transfer in chamber 39 to chamber 36. The result is that an overly rapid increase of .fuel iiow to the combustion chamber is prevented. The deceleration adjustment shown limits the motion of the piston 31 tothe left and thereby controls the amount by which the restricted orice is opened up which, in turn, controls the relative rapidity of deceleration and acceleration. Like. Wise, the acceleration control screw can be adjusted so thatpiston 31 will not move so as to presentthe complete spiral groove if it is desired to have more rapid acceleration.

A viscosity control heater coil is shown surroundingthe piston 31 which coil is connected-.to the main power supply and maybe controlledxby a thermostat located in the oil adjacent the piston 31. With this arrangement, oil viscosity at. the piston `31 and the calibration of the adjustment is maintained constant regardless of external temperatures.

A burner'blowout adjustment screw 45 may be provided to limit closing of the throttle'below that point where the burner vwill blow out. In most jet or turbine engines it is desirable to have'the fuel supply cut ofl completely when the manual control is set to its off position and yet itis not desirable that the throttle itself be permittedto moveto a position where the burner will blow out unless'such a 'position is manually selected. This creates a problem where the throttle is controlled by a remote control or servosystem; sothe burner `blowout screw isV-adjustedto. prevent :unselected burner blowout...

We also provide an automatic cut-off valve between the line I2 and combustion chamber at I3 which is spring-urged to a closed position by a light spring so that when the pressure in line I2 drops below a certain predetermined value, even though that pressure may not be zero, no fuel can ilow into the combustion chamber. Likewise, if the condition lever is set to the off position, we provide means to completely cut oiT the fuel supply by connecting a cut-off pilot so that it is moved with the selector valve. In the off position of the selector valve, the cut-off pilot valve opens a line 52 to low pressure line Ilc, branching from the main fuel supply line I5. When this occurs pressure behind the constant pressure difference valve drops rapidly and that valve is moved to the left by fuel pump pressure in line Ila. This by-passes fuel pump pressure from line I I into line Ila and back to the supply line I Il. Simultaneously pressure in the throttle outlet line I2 drops to the value at which the cutoff valve can close, so that fuel is completely out off from the combustion chamber even though the throttle itself can never be completely closed by the servo control system.

In the modification shown in Fig. 2, results similar to those just described in the first embodiment are attained except the hydraulic and electric circuits are interchanged in such a manner that the hydraulic system regulates the load to hold a selected turbine speed, whereas the temperature measuring and lag correction system regulates the fuel supply to maintain a selected absolute temperature in the combustion chamber. The constant and variable pressure pumps and associated regulators, and the action of the selector valve is like that in the previously described form. However, instead of connecting the constant and variable pressure lines to a selector shuttle valve, they connect to opposite ends cf an electrohydraulic piston assembly which we refer to as the propeller governing switch. The constant pressure line 23 communicates with a chamber 50 on one side of the propeller governor switch and the variable pressure line 24a connects to chamber 52a on the other side thereof. It will be remembei-ed that under equilibrium conditions the speed of the engine automatically attains such a value that lthe pressure in line 24a equals that in line 23, and the turbine speed necessary to cause such equalization of pressures is determined by the position of the speed -selector valve. Normally, the propeller governor switch is centered in its cylinder in the oiT position, and a pair of opposed springs tend to keep the switch in its neutral position. Each end of the switch has an arm or other support means 52 and 52a respectively which carry the movable arm of variable resistance shown schematically in the drawing. Each resistance 52 and 52a is connected to one input of the propeller pitch changing motor. In order that direction of flow to the motor will be such as to effect the necessary increase or decrease in load and in order that the amount of current iiow to the propeller motor will depend upon the amount of variation between the actual speed and the selected speed, a pair of resistances are provided in the governing switch as illustrated schematically in the drawings. The pair of resistances 54 and 5ta are connected together to one side of the power supply and each of the resistances may be engaged by its associated resistance arm 52 and 52a respectively, depending upon which way the piston is moved from neutral. A pair of stationary contact members 53 and 53a are also in position so that one of these members is engaged by the arm 52 or 52a depending upon which way the switch is off neutral, in order to complete the circuit. These fixed contact members are connected together and to the other side of the power supply. There is a small dead space at neutral to keep very small speed changes from energizing the propeller pitch motor.

The governor switch acts as follows: Assume that a speed has been selected and that turbine speed becomes greater than the selected speed. ln this case pressure in line 24a will exceed that in the constant pressure line 23 and the switch will move to the right. This will cause arm 52a to connect to engage the fixed Contact 53a so that line 53 leading to the propeller motor will be connected to the power supply. The other arm 52 will engage the resistance 54 thereby connecting line 59 from the motor to the other power supply line but through the resistance 54. The greater the displacement of the switch piston the less resistance there will be in the circuit and the more the motor will be energized. When this occurs in the assumption made, the propeller pitch will be increased, increasing the load and causing the turbine to slow down until actual and selected speeds are equal. As this occurs pressure in line 25a gradually drops until it again equals pressure in the constant pressure line 23, whereupon the governor switch piston overshoots and is rapidly restored to its neutral position and the pitch governing motor is de-energized.

An electric temperature circuit may be provided to control the throttle in response to absolute temperature within the combustion chamber in order to maintain that temperature at a preselected value regardless of the speed of the turbine. Such a circuit is described in detail in the aforesaid co-pending application, Serial No. 711,961, led Nov. 23, 1946. Instead of connecting the temperature responsive regulator to control the propeller pitch governing motor as in the rst modification, the temperature circuit energizes and regulates the action of a servomotor which positions the throttle. The throttle is similar to that shown in the previous modification except that a through passageway 43a. is provided so that there will be no fluid block at either end of the throttle to prevent its being positioned by the motor. There is a constant pressure drop system operating in conjunction with the throttle inlet and outlet which functions like that previously described. With the arrangement shown, it can be seen that if the temperature in the combustion chamber increases from the preselected value, the temperature correction system will cause the throttle motor to decrease the fuel flow into the combustion chamber until temperature therein drops back to the selected value.

There is a cut-off pilot which is connected to the temperature control lever so that when this temperature lever is set for temperature below a certain value, line 52a. is opened to inlet pressure and the constant pressure difference valve by-passes the fuel pump output causing the cutoff valve in line I3 to spring shut and prevent further flow of fuel into the combustion chamber. We contemplate that the cut-orf pilot could be connected to the condition lever instead of to the temperature control lever in order to cause the fuel supply to shut off at a certain minimum speed.

Having thus described the present invention so that others skilled in the art may be able to giocano 9. understand and practcethesame, we state that whatwe desire` to secureby Letters Patent is delinedr in what isv claimed.

What is claimed is: y

1.2 A fuel control system for an internal combustionengine comprising a pair of. hydraulic pumps arranged to be driven by the engine, one ofv said pumps being asso'ciatedwith a relief valve adjusted so that the pump forms a source of constant pressure,V the other pump being arranged to provide a source of pressure dependent upon: engine speed, a cylinder, a fuel supply system for said engine leading into and out of said cylinder, a floating piston in said cylinder for controlling the fuel supply to the engine, and conduits connecting one pump to one end of said cylinder and the other pump to the other end of said cylinder.

2. InA combination with an internal combustion engine, a source of fuel supply, a throttle in the lineA between said source and the engine, means responsive to the inlet andv outlet pressures of said' throttle to maintain a constant pressure drop across said throttle, control means for the throttle arranged to hold enginel speed constant, said` control means comprising a servo-circuit sealed from said fuel supply, said servo-circuit including constant pressure line, means whereby said constant pressure tends to open said throttle, a line the pressure of which varies with engine speed, and Vmeans whereby said variable pressure tends to close said throttle, pressures in `said lines being equal when the engine is at a predetermined speed. .v

3f. A fuel control system for an `internal combustion engine having a source of fuel supply and a fuel line, comprising a throttle means for connection in the fuel line, opposed throttle opening and closing lines for moving said throttle, a two-way control valve connected to said actuating lines, a source of fluid under constant pressure urging said control valve in one direction, a source of fluid that varies with engine speed urging said control valve in the other direction, and passageway means in said control valve arranged to connect the constant pressure line to the throttle opening line when the constant pressure exceeds the variable pressure and to connect the variable pressure line to the throttle closing line when the variable pressure exceeds the constant pressure.

4. A fuel control system for an internal combustion engine having a source of fuel supply and a fuel line, comprising a throttle means for connection in the fuel line, opposed throttle opening and closing lines for moving said throttle, a two-way control valve connected to said actuating lines, a source of fluid under constant pressure urging said control valve in one direction, a source of fluid that varies with engine speed urging said control valve in the other direction, passageway means in said control valve arranged to connect the constant pressure line to the throttle opening line when the constant pressure exceeds the variable pressure and to connect the Variable pressure line to the throttle closing line when the variable pressure exceeds the constant pressure, and means for manually adjusting one of the pressures leading to said control valve to provide a manual speed adjustment.

5. A fuel control system for an internal combustion engine having a source of fuel supply and a fuel line, comprising a throttle means for connection in the fuel line, opposed throttle opening and closing lines for moving said throttle, a twoway control valve connected to said actuating lines, a source of fluid under constant pressure urging said control valve in one direction, a source of fluid that varies with engine speedurging said control valve in the other direction, passageway means in said control valve arranged to connect the constant pressure line to the throttle opening line when the constant pressure' exceeds the variable pressure and to connect the variable pressure line to the throttle closing line when the variable pressure exceeds thexconstant pressure, and variable restriction means in one of said opposed throttle lines, the effective re'-V striction being greatest when ilow in said lines is in a direction to op'en the throttle.

6. In a fuel control system for an internal comfbustion engine, a fuel supply line vforzthe engine, a throttle in the line, opposed. hydraulic throttle actuating linesfor said`throttle, and a restriction device. in one of said throttle actuating lines, said restriction device including means movable to decrease the effective restriction in response'` to fluid ow about the device in a direction tending to rclose the throttle.

"i. In combination with an internal combustion` engine, a source of fuel under pressure for the engine, a throttle in the line between said source' and the engine, means to maintain a constant pressure drop across the throttle comprising 'a2- by-pass line for the throttle inlet line, ai by-pass valve spring-urged to close off said by-pass line', said valve having: a faceA subject to throttleainlet pressure tending to openf the by-pass, orifice means t0 permit throttle inlet pressure to slowly build up behind saidv by-pass valve, a bleed line' to bleed olf pressurev behind said icy-passl valve",l control means responsive to throttle outlet pressure to open said bleed line as throttle outlet pressure drops causing motion of said by-pass valve toward its open position, said control means closing said bleed line as throttle outlet pressure rises permitting pressure to increase behind said by-pass valve and urge it toward its closed position.

8. In combination with an internal combustion engine, a source of fuel under pressure for the engine, a throttle in the line between said source and the engine, means to maintain a constant pressure drop across the throttle comprising a by-pass line for the throttle inlet line, a by-pass valve spring-urged to close off said by-pass line, said valve having a face subject to throttle inlet pressure tending to open the by-pass, orifice means to permit throttle inlet pressure to slowly build up behind said by-pass valve, a bleed line to bleed on pressure behind said by-pass valve, control means responsive to throttle outlet pressure to open said bleed line as throttle outlet pressure drops causing motion of said by-pass valve toward its open position, said control means closing said bleed line as throttle outlet pressure rises permitting pressure to increase behind said by-pass valve and urge it towards its closed position, and manually controlled pilot means to bleed off pressure behind said by-pass valve.

9. In combination with an internal combustion engine, a source of fuel supply for the engine, a throttle in the line between said source and the engine, a out off valve in the throttle outlet line to cut olf fuel supply to the engine at a predetermined minimum pressure, by-pass means responsive to pressure in the inlet and outlet lines of the throttle to by-pass one of said lines to the source and maintain a constant pressure drop across said throttle independent of pressure variations in the inlet and outlet fuel lines of the throttle, and manually controlled by-pass pilot means connected to said rst by-pass means causing it to reduce the throttle inlet pressure whereby the throttle outlet pressure falls below the predetermined closing pressure of said cutoif valve.

10. In combination with an internal combustion engine having a burner, a source of fuel supply for the engine, a throttle in the line between said source and the engine, a remote control system for the throttle separate from the engine fuel supply and arranged to control the fuel supply to the engine, stop means preventing said throttle to close far enough to extinguish the burner in the engine, a cut off valve in the throttle outlet line to cut off fuel supply to the engine at a predetermined minimum pressure, by-pass means responsive to the inlet and outlet pressures of the throttle to maintain a constant pressure dropacross said throttle thereby insuring uniformity of engine condition control independent of pressure variations in the inlet and outlet fuel lines of the throttle, and manually controlled pilot means connected to said constant pressure drop means causing it to reduce throttle inlet pressure whereby said by-pass means reduces the throttle outlet pressure below the critical closing pressure of said cut-off valve.

11. A fuel control system for an internal combustion engine comprising a pair of hydraulic pumps arranged to be driven by the engine, one of said pumps being associated with a relief valve adjusted so that the pump forms a source of constant pressure, the other pump being arranged to provide a source of pressure dependent upon engine speed, a cylinder, a fuel supply system for said engine leading into and out of said cylinder, a floating piston in said cylinder for controlling the fuel supply to the engine, conduits connecting one pump to one end of said cylinder and the other pump to the other end of said cylinder, and fuel by-pass means responsive to fuel pressure in the inlet and outlet lines of the cylinder to maintain a constant pressure drop across said oating piston.

ALVIN A. ROOD.

JOHN F. CAMPBELL.

REFERENCES CITED The following references are of record in' the le of this patent:

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